The leukotrienes constitute a group of locally acting hormones, produced in living systems from arachidonic acid. The major leukotrienes are Leukotriene B.sub.4 (abbreviated as LTB.sub.4), LTC.sub.4, LTD.sub.4, and LTE.sub.4. The biosynthesis of these leukotrienes begins with the action of the enzyme 5-lipoxygenase on arachidonic acid to produce the epoxide known as Leukotriene A.sub.4 (LTA.sub.4), which is converted to the other leukotrienes by subsequent enzymatic steps. Further details of the biosynthesis as well as the metabolism of the leukotrienes are to be found in the book Leukotrienes and Lipoxygenases, ed. J. Rokach, Elsevier, Amsterdam (1989). The actions of the leukotrienes in living systems and their contribution to various diseases states are also discussed in the book by Rokach.
European patent applications 462,813 and 462,831 disclose pyran derivatives which are claimed to be inhibitors of 5-lipoxygenase. These compounds differ from the present invention in that Q always contains a nitrogen heterocycle, and the nature of the link (A.sup.1 -X .sup.1) is different from a corresponding unit (X.sup.3) in the present compounds. Crawley discloses the structure 3 as an inhibitor of 5-lipoxygenase but it too differs substantially from the present invention in that the present compounds most closely related to structure 3 contain a highly rigid bicyclic ring structure in place of the tetrahydropyran ring of 3. ##STR2##